text: The lotus flower has been known as a symbol of purity in some Asian cultures. The lotus leaves (Nelumbo nucifera) are water-repellent and poorly adhesive which keep them free from contamination or pollution even being immersed in dirty water. This ability, called self-cleaning, shields the plant from dirt and pathogens and plays a vital role in providing resistance towards invading microbes. Indeed, numerous spores and conidia of pathogenic life forms, mainly fungi, need water for germination and taint leaves within the first signs of water. It had been a curiosity how lotus flower could remain clean even in muddy water, until German botanists, Barthlott and Neinhuis, introduced the unique dual structure of leaves with the help of a scanning electron microscopy (SEM). Papillose epidermis cells carpet the exterior of a plant, particularly the leaf. These cells generate papillae or microasperties which make surface very rough. On top of microscale roughness, the papillae surface is superimposed with nanoscale asperities consisting of three-dimensional (3-D) hydrophobic hydrocarbons: epicuticular waxes. Basically, the plant cuticle is a composite material composed of a network of cutin and low surface energy waxes, designed at different hierarchical levels. The various leveled surface of lotus leaves is made out of convex cells (looks like bumps) and a much smaller layer of waxy tubules. The water beads on plant leaves rest on the apex of the nanofeatures since air is enclosed in the valley of convex cells which minimizes the contact area of water droplet. Hence, the lotus leaves represent remarkable superhydrophobicity. Static contact angle and contact angle hysteresis of the lotus leaf are determined around 164° and 3°, respectively. With small tilting angles, water droplets on the leaf roll off and take any dirt or contaminant along, leading to self-cleaning. The ability of drops to form and roll off, depends not only on hydrophobicity, but also on contact angle hysteresis.
  In plants world, the lotus leaf is not the only example of natural superhydrophobic surfaces. For instance, taro (Colocasia esculenta) leaves were found to exhibit self-cleaning behavior, too. They have a binary roughness built up by averagely 10 µm elliptical protrusions in diameter and nano-sized pins. India canna (Cannageneralis bailey) leaves and the rice leaves (whatever the kind of rice) also represent superhydrophobicity, arising from the hierarchical surface morphology.